Bad service

I have a bad experience with them as I sold my car two years ago and I cancelled the contract and paid the fees for cancellation and just now last November 2024 they commenced debiting my account , I tried to stop the debit order but standard bank said they can not cancel the debit order because they have my bank details so they can always go and debit . I have the reference number of the letter that I wrote when I cancelled which is 136****0. The letter was dated 14 July 2023.